This project is a randomized controlled trial to compare the efficacy of two interventions- one based on Acceptance and Commitment Therapy (ACT) and one based on Self-Regulation (SR)- and a control group (called weight loss only (WLO)) on 24-month weight loss outcomes. All participants will first participate in an initial 4-month standard behavioral weight loss program. Participants will be randomized into 1 of 3 groups and receive a 3-part workshop; the ACT workshop will teach ACT skills including acceptance and mindfulness techniques designed to promote behavior change and health behavior persistence consistent with one's core values. The SR program will focus on self-regulation, regular weighing, and modeling behavior on successful maintainers. The WLO group will receive a control workshop focused on cooking demonstrations and general nutrition topics.The primary outcome is weight loss at 24 months. The secondary outcome is change in psychological flexibility, a critical component of ACT interventions and a potential innovative mediating mechanism. Primary Hypothesis: At 24 months, the ACT group will show significantly greater weight loss as compared to the SR and WLO groups.

Inclusion Criteria:

• BMI 27.5-40
• Age 30-65

Exclusion Criteria:

• currently participating in a weight loss program
• pregnant or planning to become pregnant
• medical condition that would preclude physical activity
• terminal illness
• plans to relocate
• history of substance abuse or psychological problems that are judged by the investigators to be likely to interfere with study participation